Fuel reformer

ABSTRACT

Provided is a fuel reforming apparatus wherein vacuum reforming tubes ( 13 ) are accommodated in a flow path ( 12 ) between an inner cylinder ( 9   a ) of a heat-insulating vessel ( 9 ) and a furnace flue ( 11 ) arranged in the inner cylinder ( 9   a ). Formed between the furnace flue ( 11 ) and a guide cylinder ( 21 ) accommodated in the furnace flue ( 11 ) is a gap though which combustion gas ( 28 ) generated in a combustor ( 10 ) is raised. A helical plate ( 22 ) is arranged in the flow path ( 12 ) such that the combustion gas ( 28 ) lowered in the flow path ( 12 ) flows across the reforming tubes ( 13 ). Thus, red heating of the furnace flue can be sufficiently conducted to sufficiently heat the reforming tubes through radiation heat transfer. As a result, heat transfer areas of the reforming tubes may be made smaller to reduce in size the reforming tubes. Since upper ends of the reforming tubes are not exposed to high temperature and the combustion gas lowered between the inner cylinder of the vessel and the furnace flue has no deflections in flow, heat inputs to the respective reforming tubes become uniform, leading to improvement in performance of and reduction in size of the reformer.

TECHNICAL FIELD

The present invention relates to a fuel reforming apparatus.

BACKGROUND ART

In general, a fuel cell is such that, inversely to electrolysis ofwater, hydrogen is coupled with oxygen and electricity and heatgenerated thereupon are taken out. Because of their higher electricitygeneration efficiency and adaptability to environment, fuel cells havebeen actively developed for household-fuel-cell cogeneration systems andfuel-cell-powered automobiles. Hydrogen as fuel for such fuel cells isproduced by reforming, for example, petroleum fuel such as naphtha orkerosene or city gas through a reformer.

FIG. 1 shows a whole system for a residential type polymer electrolytefuel cell (PEFC) as an example of an installation with a reformer inwhich reference numeral 1 denotes a reformer; 2, a water vaporizer tovaporize water into water vapor through heat of exhaust gas from thereformer 1; 3, a primary fuel gasifier to gasify primary fuel such asnaphtha through heat of the exhaust gas; 4, a desulfurizer todesulfurize source gas to be fed to the reformer 1; 5, a low-temperatureshift converter to lower the reformed gas from the reformer 1 to arequired temperature (approximately 200-250° C. or so) through coolingwater so as to change CO and H₂O into CO₂ and H₂; 6, a selectiveoxidation CO remover which removes CO by an oxidation reaction fromreformed gas passed through the shift converter 5 controlled by coolingwater; 7, a humidifier to humidify the reformed gas having passedthrough the CO remover 6; and 8, a PEFC with a cathode 8 a and an anode8 b.

In the installation shown in FIG. 1, water is vaporized by the vaporizer2 into water vapor while primary fuel such as naphtha is gasified by thegasifier 3 into source gas. The source gas mixed with the water vapor isguided to the desulfurizer 4, and the source gas desulfurized in thedesulfurizer 4 is guided to the reformer 1. The gas reformed by thereformer 1 is guided via the shift converter 5, CO remover 6 andhumidifier 7 to the anode 8 b of PEFC 8 while the air is guided throughthe humidifier 7 to the cathode 8 a of the PEFC 8, thereby generatingelectric power. Anode off-gas from the anode 8 b is re-utilized as fuelgas in the reformer 1 while the water from the cathode 8 a is utilizedas cooling water for the PEFC 8, CO remover 6 and shift converter 5 andas part of the water vapor to be mixed with the source gas.

Conventionally, the reformer 1 and its associated instruments or thevaporizer 2, gasifier 3, desulfurizer 4, shift converter 5 and COremover 6 are assembled as a unit into a fuel reforming apparatus. Assuch fuel reforming apparatus, for example, a burner combustion typeapparatus as disclosed in JP 2003-327405 A has been proposed.

Such fuel reforming apparatus is shown in FIGS. 2 and 3 in which partssimilar to those shown in FIG. 1 are designated by the same referencenumerals. In the fuel reforming apparatus shown in FIGS. 2 and 3, theunit of the reformer 1 with its associated instruments (the vaporizer 2,gasifier 3, desulfurizer 4, shift converter 5 and CO remover 6) iscovered with and enclosed by a vacuum heat-insulating vessel 9 withinner and outer cylinders 9 a and 9 b and a vacuum heat-insulating layer9 c between them, thereby providing the fuel reforming apparatus.

In the above-mentioned burner combustion type apparatus, the innercylinder 9 a itself of the vessel 9 is utilized as a part of thereformer 1, and a furnace flue 11 is arranged centrally inside the innercylinder 9 a for flow of the combustion gas from a combustor 10therethrough; formed between the furnace flue 11 and the inner cylinder9 a is a flow path 12 of the combustion gas in which a plurality of (sixin FIG. 3) reforming tubes 13 are arranged side by side and are chargedwith reforming catalysts (not shown) through which source gas flows forreforming thereof, thereby providing the reformer 1. Each of thereforming tubes 13 is of a double-walled tube structure with inner andouter tubes 13 a and 13 b such that the source gas is raised up in aspace between the tubes 13 a and 13 b for heat exchange with thecombustion gas, is returned back at upper ends of the tubes and islowered in a space inside the inner tube 13 a.

The furnace flue 11 of the reformer 1 is connected to an upper end of abase inner cylinder 16 standing from a base plate 14. A lower end of thevessel 9 is detachably and sealingly connected, via connecting means(not shown) such as bolts and nuts, to an upper end of a base outercylinder 15 short in length and standing from an outer periphery of thebase plate 14. The associated instruments of the reformer 1 or thevaporizer 2, gasifier 3, desulfurizer 4, shift converter 5 and COremover 6 are arranged in a cylindrical space 17 which is defined by thebase plate 14, the base inner and outer cylinders 16 and 15 and theinner cylinder 9 a of the vessel 9 and which is communicated with theflow path 12 of the combustion gas.

The base inner cylinder 16 is interiorly formed with an air flow path 18to feed air to the combustor 10. Arranged axially of the cylinder is afuel gas supply pipe 19 to feed fuel gas such as anode off gas to thecombustor 10. Upon startup, a combustion-fuel supply pipe 20 is adaptedto feed fuel for combustion to the combustor 10.

In the fuel reforming apparatus shown in FIG. 2, the construction workof the heat insulating layer 9 c is completed merely by enclosing theunit with the vacuum heat-insulating vessel 9. As a result, time andlabor for the construction work of the heat insulating layer 9 c aredrastically relieved. Moreover, whenever maintenance such as replacementof catalysts in the reformer 1 or inspection is to be conducted, merelyopening the vessel 9 will suffice, leading to prompt operation.

Use of the vessel 9 having the vacuum heat-insulating layer 9 c betweenthe inner and outer cylinders 9 a and 9 b remarkably enhances the heatinsulating performance so that decrease in volume of the heat insulatinglayer 9 c can be attained and the apparatus can be made compact in sizewhile heat dissipation is suppressed to improve thermal efficiency.

The interior of the inner cylinder 9 a of the vessel 9 is utilized asthe flow path 12 of the combustion gas for the reformer 1, which bringsabout simplification in structure of the whole apparatus and thusreduction in cost. The reformer 1 comprises the furnace flue 11 havingcombustion gas from the combustor 10 flowing therethrough and the pluralreforming tubes 13 arranged side by side in the flow path 12 of thecombustion gas between the furnace flue 11 and the inner cylinder 9 a ofthe vessel 9 and having reforming catalysts charged therein for flowingof the source gas therethrough for reforming thereof, which makes itpossible to shorten in length the reformer 1 through utilization of themultiple reforming tubes 13 and utilization of radiant heat transfer dueto high-temperature combustion in the combustor 10, with theadvantageous result that the associated instruments such as thevaporizer 2, gasifier 3, desulfurizer 4, shift converter 5 and COremover 6 can be arranged beneath the reformer 1 so as to decrease inheight the fuel reforming apparatus.

In a normal operation, the reformer 1 is fed with the primary fuel; thecombustion gas from the burnt fuel gas is heat exchanged with theprimary fuel in the reformer 1, vaporizer 2 and gasifier 3 and islowered in temperature into about 200° C. or temperature level ofreaction in the shift converter 5 and in the CO remover 6, so that thereis no fear of unnecessary heat exchange occurring even in an instancewhere reactors such as the shift converter 5 and the CO remover 6 arenakedly arranged in the cylindrical space 17 which is the flow path ofthe combustion gas.

Thus, reduction in size of the apparatus and increase in heat efficiencycan be attained; labor and time of the construction work for the heatinsulating layer 9 c can be drastically reduced; and maintenance can bereadily carried out.

As mentioned above, the burner combustion type reforming apparatus shownin FIGS. 2 and 3 has various excellent advantages. However, thecombustion gas is raised up through the furnace flue 11 with a greatersectional area so that the furnace flue 11 cannot be sufficiently redheated through convective heat transfer, failing to efficiently conductradiation heat transfer to the reforming tubes 13. Therefore, thereforming tubes 13 must have increased surface areas (heat transferareas) and cannot be made sufficiently compact in size.

The combustion gas is not sufficiently decreased in temperature evenwhen it reaches an upper end of the furnace flue 11. Therefore, thecombustion gas, which is returned back at the upper end of the furnaceflue 11 into the flow path between the furnace flue 11 and the innercylinder 9 a of the vessel 9, is high in temperature so that upper endsof the reforming tubes 13 arranged in the flow path between the innercylinder 9 a and the furnace flue 11 are exposed to high temperature.Therefore, the reforming tubes must be made from heat-resisting alloy,leading to increase in cost.

Moreover, the combustion gas lowered in the flow path between thefurnace flue 11 and the inner cylinder 9 a of the vessel 9 flows rightdown along the reforming tubes 13 so that it has less heat transferefficiency and may have deflections in flow; as a result, heat inputs ofthe respective reforming tubes 13 may become nonuniform, leading tolowered performance of the reformer 1 and difficulty in sufficientlyreducing in size of the reforming tubes 13.

The invention was made in view of the above and has its object toprovide a fuel reforming apparatus which facilitates convective heattransfer by the combustion gas flowing in the furnace flue so as tosufficiently red heat the furnace flue and sufficiently heat thereforming tubes through the radiation heat transfer, so that the heattransfer area of each of the reforming tubes may be made smaller tofurther reduce in size the reforming tubes; the upper end of thereforming tube may be prevented from being exposed to high temperatureso as to allow the reforming tubes made from material other thanheat-resisting alloy; the combustion gas flowing down through the flowpath between the furnace flue and the inner cylinder of the vacuumheat-insulating vessel is prevented from having deflections in flow;heat inputs of the respective reforming tubes are made uniform, wherebythe reformer can be improved in performance and reduced further in size.

SUMMARY OF THE INVENTION

The invention is directed to a fuel reforming apparatus whereinreforming tubes are accommodated in a flow path between an innercylinder of a vessel and a furnace flue arranged in the inner cylinder,combustion gas generated in a combustor and raised up in said furnaceflue being lowered in said flow path so as to reform source gas flowingin a reformer, characterized in that formed between said furnace flueand a guide cylinder accommodated in the furnace flue is a gap thoughwhich the combustion gas generated in the combustor for introductiontoward an upper end of said flow path is raised.

The invention is further directed to a fuel reforming apparatus whereinreforming tubes are accommodated in a flow path between an innercylinder of a vessel and a furnace flue arranged in said inner cylinder,combustion gas generated in a combustor and raised up in said furnaceflue being lowered in said flow path so as to reform source gas flowingin a reformer, characterized in that a helical plate is arranged in saidflow path such that the combustion gas returned back at an upper end ofsaid furnace flue and lowered in said flow path flows across saidreforming tubes.

The invention is still further directed to a fuel reforming apparatuswherein reforming tubes are accommodated in a flow path formed betweenan inner cylinder of a vessel and a furnace flue arranged in said innercylinder, combustion gas generated in a combustor and raised up in saidfurnace flue being lowered in said flow path so as to reform source gasflowing in a reformer, characterized in that formed between said furnaceflue and a guide cylinder accommodated in the furnace flue is a gapthrough which the combustion gas generated in the combustor forintroduction toward an upper end of said flow path is raised, a helicalplate being arranged in said flow path such that the combustion gasreturned back at an upper end of said furnace flue and lowered in saidflow path flows across said reforming tubes.

In the invention, the combustion gas is raised through the gap betweenthe furnace flue and the guide cylinder accommodated in the furnace flueto red heat the furnace flue through convective heat transfer, thecombustion gas being returned back at the upper end of the furnace flueand lowered while guided by the helical plate arranged in the flow pathdefined by the inner cylinder and the furnace flue. Thus, the reformingtubes are heated through radiation heat transfer of the furnace flue andare also heated through convective heat transfer of the combustion gaswhich is lowered to flow across the reforming tubes by the guidance ofthe helical plate.

According to a fuel reforming apparatus of the invention, combustion gasis raised up in the narrow gap between the furnace flue and the guidecylinder and in parallel with the source gas flowing in the reformingtubes so as to red heat the furnace flue, whereby radiation heattransfer can be efficiently conducted from the furnace flue to thereforming tubes. Thus, the surface areas (heat transfer areas) of thereforming tubes can be reduced and the reforming tubes can be madecompact in size.

Because of the reforming tubes being not exposed to high temperature,the reforming tubes may be made from usual stainless steel, leading todecrease in cost.

The combustion gas lowered in the space between the furnace flue and theinner cylinder of the vacuum heat-insulating vessel is guided by thehelical plate to flow diametrically across all of the reforming tubes,so that flow rate of the combustion gas is high in comparison with aninstance where the combustion gas flows right down with no helicalplate, thereby obtaining heat transfer efficiency about four times asgreat as that of latter. Thus, the convective heat transfer isfacilitated; heat transfer is made to all of the reforming tubes withuniform gas flow rate so that heat inputs to the respective reformingtubes become uniform, resulting in lack of heat unevenness; thus, thereformer can obtain high reforming performance and the reforming tubesmay be compact in size.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a whole system of an example of an installationwith a reformer;

FIG. 2 is a vertical section of an example of a burner combustion typefuel reforming apparatus;

FIG. 3 is a view looking in the direction of arrows III in FIG. 2;

FIG. 4 is a vertical section of an embodiment of a fuel reformingapparatus according to the invention; and

FIG. 5 is a view looking in the direction of arrows V in FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the invention will be described on the basis of thedrawings.

FIGS. 4 and 5 illustrate an embodiment of the invention in which partssimilar to those in FIG. 2 are represented by the same referencenumerals. A fuel reforming apparatus according to the embodiment, whichis similar in fundamental structure to the conventional apparatus shownin FIG. 2, is characteristic in that, as shown in FIG. 4, a guidecylinder 21 is arranged coaxially of and extends through a furnace flue11 beyond an upper end of the furnace flue 11 and that a helical plate22 is arranged in a flow path 12 defined by the furnace flue 11 and aninner cylinder 9 a of a vacuum heat-insulating vessel 9 so as tosurround reforming tubes 13.

The guide cylinder 21 is made from usual stainless steel, is hollow inits interior and is closed at its lower end. Mounted on an upper end ofthe guide cylinder 21 is a guide plate 23 which is larger in diameterthan the furnace flue 11; combustion gas raised up in a gap between thefurnace flue 11 and the guide cylinder 21 is returned back by the guideof guide plate 23 into the flow path 12 between the inner cylinder 9 aand the furnace flue 11.

In the drawings, reference numeral 15 a denotes a discharge portconnected to a side of the base outer cylinder 15; 24, an air supplypipe; 25, fuel gas which is anode off-gas; 26, combustion fuel such asnaphtha; 27, air; 28, combustion gas; 29, source gas which is beingreformed; and 30, exhaust gas. Though not shown, the primary fuel suchas naphtha is adapted to be introduced into the primary fuel gasifier 3;water is adapted to be introduced into a water vaporizer 2; and thereformed gas is adapted to be introduced via a selective oxidation COremover 6 and a humidifier 7 shown in FIG. 1 into an anode 8 b of a PEFC8.

Next, the mode of operation of the above embodiment will be describedalso in conjunction with FIG. 1.

When electric power is to be generated in the PEFC 8 shown in FIG. 1,primary fuel is required to be reformed by a reformer 1. To this end, inthe fuel reforming apparatus shown in FIG. 4, water is vaporized in thevaporizer 2 into water steam and the primary fuel such as naphtha isgasified in the gasifier 3 into source gas. The source gas mixed withthe water steam is introduced into the desulfurizer 4. Afterdesulfurized in the desulfurizer 4, the source gas 29 is guided andraised up between outer and inner tubes 13 b and 13 a of reforming tubes13 in the reformer 1, is returned back at the upper ends of thereforming tubes 13 and is lowered in the inner tube 13 a; during suchupward and downward movements, as detailedly explained hereinafter, itis heated by the combustion gas 28 so as to be reformed.

On the other hand, the fuel gas 25, the combustion fuel 26 and the airfrom the air supply pipe 24 are burnt in the combustor 10 to generatehigh-temperature (about 1200° C.) combustion gas 28 which is raised upin the narrow gap between the furnace flue 11 and the guide cylinder 21uniformly and at high flow rate without having deflections in flow. Theupward flow of the combustion gas 28 is in parallel with the source gas29 flowing upward or downward in the reforming tubes 13. Thus, theupward flow of the combustion gas 28 in the narrow gap between thefurnace flue 11 and the guide cylinder 21 and in parallel with thesource gas 29 flowing in the reforming tubes 13 accelerates convectiveheat transfer by the combustion gas 28 to red heat the furnace flue 11,the reforming tubes 13 being heated by radiation heat transfer of thefurnace flue 11.

The combustion gas 28 having reached the upper end of the narrow gapbetween the furnace flue 11 and the guide cylinder 21 is returned backby the guide plate 23 and is lowered in the flow path 12 between theinner cylinder 9 a and the furnace flue 11 helically along the helicalplate 22 to flow diametrically across the reforming tubes 13 and heatthe same through convective heat transfer; then, it passes through thecylindrical space 17 where the vaporizer 2, desulfurizer 4, shiftconverter 5, gasifier 3 and CO remover 6 are accommodated and isdischarged outside as the exhaust gas 30 via the combustion gasdischarge port 15 a on the lower end of the base outer cylinder 15.

The source gas 29 flowing up and down in the reforming tubes 13 isheated through radiation heat transfer of the furnace flue 11 heated bythe combustion gas 28 and is also heated through convective heattransfer of the combustion gas 28 which is lowered to flow diametricallyacross the reforming tubes 13 helically along the helical plate 22 inthe flow path 12 between the inner cylinder 9 a and furnace flue 11,whereby it is reformed.

According to the embodiment, the combustion gas 28 is raised up in thenarrow gap between the furnace flue 11 and the guide cylinder 21 and inparallel with the source gas 29 flowing in the reforming tubes 13 so asto red heat the furnace flue 11 through convective heat transfer, sothat efficient radiation heat transfer can be conducted to the reformingtubes 13 by the furnace flue 11. Therefore, the surface areas (heattransfer areas) of the reforming tubes 13 can be reduced and thereforming tubes 13 can be made compact in size in comparison with thosein the fuel reforming apparatus shown in FIG. 2.

The combustion gas 28 heats the furnace flue 11 through convective heattransfer, and the furnace flue 11 h heats through radiation heattransfer a low-temperature region with great heat input required whichis adjacent to an inlet of the reformer 1 below a lower end of thefurnace flue 11, so that temperature of the combustion gas 28 at theupper end of the gap between the furnace flue 11 and the guide cylinder21 is lowered than the combustion temperature (1200° C.) of thecombustor 10 into the order of 800° C. which is sufficient forreforming. Therefore, the reforming tubes 13 may not be made from costlyheat-resisting alloy and may be made from usual stainless steel, leadingto cost-down of the fuel reforming apparatus.

The combustion gas 28 lowered in the flow path 12 between the innercylinder 9 a of the vessel 9 and the furnace flue 11 is guided by thehelical plate 22 to flow diametrically across all the reforming tubes 13so that the flow rate of the combustion gas 28 is high in comparisonwith an instance where the combustion gas flows right down with nohelical plate 22, so that great heat transfer efficiency is obtainedwhich is about four times as great as that of the latter. Thus,convective heat transfer is facilitated and is made to all of thereforming tubes 13 at uniform gas flow rate, so that input heats of therespective reforming tubes 13 become uniform with no heat unevenness. Asa result, the reformer 1 can obtain high reforming performance.Moreover, the reforming tubes 13 have great heat transfer efficiency,which fact also contributes to reduction in size of the reforming tubes13.

The gas reformed in the reformer 1 passes through the low-temperatureshift converter 5 and the selective oxidation CO remover 6 and is fedvia the lower end of the base outer cylinder 15 to outside of the fuelreforming apparatus and then into the humidifier 7 shown in FIG. 1; itfurther introduced via the humidifier 7 to the anode 8 b of the PEFC 8while the air is introduced via the humidifier 7 to the cathode 8 a ofthe PEFC 8, thereby generating electricity.

It is to be understood that, in a fuel reforming apparatus according tothe invention, various changes and modifications may be effected withoutdeparting from the spirit of the invention. For example, the selectiveoxidation CO remover may be substituted with a methanator which utilizesso-called methanation reaction.

INDUSTRIAL APPLICABILITY

As is clear from the foregoing, a fuel reforming apparatus according tothe invention is effective as a fuel reforming apparatus for reformingthe primary fuel such as methanol, city gas, naphtha or kerosene to befed to the fuel cell. Since surface areas (heat transfer areas) ofrespective reforming tubes can be reduced, the apparatus is especiallyeffective as a fuel reforming apparatus which can be made compact insize; it is effective as a fuel reforming apparatus which is low incost; furthermore, it is effective as fuel reforming apparatus which canobtain high reforming performance as convective heat transfer isfacilitated and conducted to all of the reforming tubes with uniform gasflow rate so that input heats of the respective reforming tubes becomeuniform with heat unevenness being eliminated.

1. A fuel reforming apparatus wherein reforming tubes are accommodatedin a flow path between an inner cylinder of a vessel and a furnace fluearranged in said inner cylinder, combustion gas generated in a combustorand raised up in said furnace flue being lowered in said flow path so asto reform source gas flowing in a reformer, characterized in that formedbetween said furnace flue and a guide cylinder accommodated in thefurnace flue is a gap through which the combustion gas generated in thecombustor for introduction toward an upper end of said flow path israised.
 2. A fuel reforming apparatus wherein vessel wherein reformingtubes are accommodated in a flow path between an inner cylinder of avessel and a furnace flue arranged in said inner cylinder, combustiongas generated in a combustor and raised up in said furnace flue beinglowered in said flow path so as to reform source gas flowing in areformer, characterized in that a helical plate is arranged in said flowpath such that the combustion gas returned back at an upper end of saidfurnace flue and lowered in said flow path flows across said reformingtube.
 3. A fuel reforming apparatus wherein reforming tubes areaccommodated in a flow path formed between an inner cylinder of a vesseland a furnace flue arranged in said inner cylinder, combustion gasgenerated in a combustor and raised up in said furnace flue beinglowered in said flow path so as to reform source gas flowing in areformer, characterized in that formed between said furnace flue and aguide cylinder accommodated in the furnace flue is a gap through whichthe combustion gas generated in the combustor for introduction forwardan upper end of said flow path is raised, a helical plate being arrangedin said flow path such that the combustion gas returned back at an upperend of said furnace flue and lowered in said flow path flows across saidreforming tubes.